Below, Dr. Trisha Pasricha shares five key insights from her new book, You’ve Been Pooping All Wrong: How to Make Your Bowel Movements a Joy.
Trisha is a gastroenterologist at Beth Israel Deaconess Medical Center, where she directs the Institute for Gut-Brain Research. She is also an assistant professor at Harvard Medical School and writes the “Ask a Doctor” column for The Washington Post.
What’s the big idea?
What if the gut isn’t just a passive tube that moves food through your body, but an intelligent organ? 40 percent of Americans say their daily lives are disrupted by their bowel habits. And yet almost no one talks about it, because we’ve been taught since childhood to treat our gut health as shameful, private, and something to distance ourselves from as quickly as possible. That silence has a cost. And this book is about ending it.
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1. Your gut is a brain.
Most of us think of the brain in our heads as the command center that runs the show. But your gastrointestinal tract contains hundreds of millions of neurons—more than your entire spinal cord—forming what scientists call the enteric nervous system. This brain in your gut can sense the environment, process information, and coordinate complex activity entirely on its own, without any input from the brain in your skull.
The gut came before the brain, evolutionarily. Even jellyfish, despite having no appreciable brain in their translucent heads, do have a primitive version of an enteric nervous system and can’t survive without it. The gut largely communicates with the brain via a superhighway called the vagus nerve, but it is anything but a passive recipient of instructions. It has its own reflexes, its own electrical rhythm, and its own agenda.
I discovered this firsthand in high school. I had a hunch that psychological stress—the kind you feel when you’re telling a lie—would change the electrical activity of the stomach, explaining that visceral “sinking feeling” people describe when they’re anxious. Using an electrogastrogram, a device that measures the stomach’s electrical rhythm through electrodes on the abdomen, I tested whether telling a lie would disrupt it. It did, quite reliably. The stomach’s electrical rhythm went from a predictable three cycles per minute to pure chaos. That discovery won at the Intel International Science Fair in 2005, and it set the direction for my entire career.
The gut does a bit more than just process your lunch. The gut and the brain have been in dialogue for hundreds of millions of years and we are only beginning to decipher the conversation.
2. Parkinson’s disease may originate in your gut.
I started noticing a certain pattern early in my gastroenterology training. My patients with Parkinson’s disease didn’t just have neurological symptoms. They had gut symptoms such as severe constipation, nausea, and bloating. And when I asked them when those gut symptoms started, the answer was uncanny: often not after their Parkinson’s diagnosis, but years before. Sometimes decades before.
This wasn’t a coincidence. Studies of tens of thousands of patients have confirmed that gut trouble can precede tremors and rigidity by years. Even Dr. James Parkinson himself (the physician for whom the disease is named) suspected the gut had more importance than met the eye.
“Studies of tens of thousands of patients have confirmed that gut trouble can precede tremors and rigidity by years.”
What’s happening, according to a now well-supported theory, is that a misfolded protein called alpha-synuclein—the hallmark of Parkinson’s disease—may originate in the neurons inside the gut wall, then travel up the vagus nerve to reach the brain. Tellingly, patients who had their vagus nerve surgically severed decades earlier turned out to be less likely to develop Parkinson’s disease later in life.
My own lab published a study in JAMA Network Open in 2024 looking at records of over 9,000 patients. People with injuries to the lining of their stomachs and small bowels had a 76 percent higher risk of later developing Parkinson’s.
But this matters beyond Parkinson’s because the same principle—that disturbances in the gut can signal changes in the brain years before anyone recognizes a disease—is now being explored in Alzheimer’s, autism, and conditions we’ve always thought had nothing to do with the gut. The gut may be an early warning system that medicine has largely ignored. The earlier we learn to read it, the better our chances of intervening before the damage reaches the brain.
3. The 100 trillion microbes in your gut shape more than digestion.
Inside your gut live over 100 trillion microorganisms. We call this community and their genetic material the microbiome, and for most of the 20th century, medicine basically ignored it. We now know that was a catastrophic oversight.
Your microbiome begins forming at birth and is largely set by the time you’re three or four years old. As an adult, one of the biggest levers you have to change its composition is your diet. These microbes ferment what we can’t digest, produce compounds that influence everything from our immune system to our gut lining, and send signals via the enteric nervous system all the way back to the brain.
Here’s an unexpected example of just how far that influence reaches. Researchers at the University of Pennsylvania wanted to understand why some people are naturally motivated to exercise and others simply aren’t. They studied hundreds of genetically diverse mice and measured their exercise capacity. Some ran like athletes. Others barely moved. Genetics explained almost none of the difference. But one factor predicted performance better than everything else combined: the gut microbiome.
“The “runner’s high”—that surge of motivation during exercise—doesn’t originate entirely in the brain.”
To confirm this, they wiped out all the mice’s microbiomes with antibiotics. The previously high-performing runners dropped their activity by 50 percent. Then the researchers traced the mechanism: proteins from the microbiome were signaling neurons in the gut, which sent messages up to the brain, boosting dopamine and the drive to move. The “runner’s high”—that surge of motivation during exercise—doesn’t originate entirely in the brain. It’s being initiated in the gut. That study was published in Nature in 2022.
We are not independent organisms powered purely by willpower and genetics. We are ecosystems. And the 100 trillion organisms living inside us have a much larger vote in how we feel, how we move, and how our brains function than we give them credit for.
4. Modern life has set you up to poop all wrong.
When I tell patients that they’ve been pooping wrong, I don’t mean it as an insult. In some ways, I mean it more as an indictment of modern life.
A successful bowel movement requires three things working in concert:
- Propulsion — the muscular contractions that push stool forward.
- Pliability — soft enough stool to actually move.
- Pelvic floor muscles — to relax and open at the right moment.
I call these the Three P’s. And modern life has found a way to sabotage all three.
The Western diet gives most people inadequate fiber. Over 90 percent of Americans don’t meet the daily recommendation, which means hardened stool. We rush our mornings, which means we’re leaving home without availing ourselves of the body’s natural bowel movement window: the colon surges in activity during the early morning and again after meals, thanks to a reflex wired into us for millions of years. But we too often ignore the signal, defer it, and then wonder why nothing happens on command.
And then there’s the toilet itself. The modern porcelain throne positions you at a 90-degree angle, leaving the sling-like muscle called the puborectalis partially contracted, creating a kink in the rectal tube. It is, essentially, your body stepping on its own hose. Squat—knees above hips, the position our ancestors used—and that muscle fully relaxes. The tube straightens. And no, you don’t need to squat fully. All it takes is a footstool or a discreet stack of books.
Knowledge gaps like these aren’t trivial. They cost people real quality of life, not to mention consequences you really don’t want. My own research found that unnecessarily prolonged time sitting on the toilet—you know exactly what I mean: the kind that happens when you’re distracted by your smartphone—is associated with a significantly higher risk of hemorrhoids.
The list of our misguided bathroom habits goes on and on. But the issue is that most people have never questioned whether they’re doing this right. The answer, I find almost universally, is that they’re not.
5. Gut trauma can cause depression and anxiety.
For as long as most of us have been alive, the relationship between the gut and mental health has been framed one way: stress causes stomach problems. You’re anxious, so your gut acts up. But what if, in many cases, we have the direction entirely backward?
My father, Dr. Jay Pasricha, now Chair of Medicine at the Mayo Clinic and one of the founders of neurogastroenterology, spent years designing experiments to test exactly this. His lab took two groups of rats. One received a mild irritant to their colon shortly after birth. The other experienced nothing unusual. Then both groups were raised identically: the same food, the same environment, the same social conditions.
When the rats were fully grown, the control group barely noticed mild gut distension. But the rats whose guts had been briefly disturbed shortly after birth responded completely differently — nerve impulses from the colon spiked, and the rats contracted their abdominal muscles in discomfort at volumes the others found imperceptible. The gut, during that early vulnerable window, had been permanently sensitized.
But the most unsettling finding was what came next. Those same rats were now depressed and anxious. When placed in water, they barely tried to swim to safety. In open fields, they clung to the edges, afraid. And when his lab cut their vagus nerve (that highway connecting gut to brain), the depression and anxiety disappeared. The gut, traumatized early in life, had been sending distress signals to the brain all along.
“The gut, during that early vulnerable window, had been permanently sensitized.”
What this means is profound. When someone comes to me with depression or anxiety and gut symptoms—and many of my patients do—the gut is not a sidebar. It may be where the story started. The idea that “it’s all in your head” is not just unhelpful. In many cases, it’s directionally wrong. The signal is coming from below.
We have spent a century building the architecture of mental health care entirely from the neck up. What we’re learning is that we need to start listening a bit further south.
The gut is the most underestimated organ in the human body. Once you understand it, everything changes—not just what happens in your bathroom, but how you think about your body, your mood, your health, and the conditions that medicine has long struggled to explain.
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